Without limiting the scope of the invention, its background is described in connection with semiconductor-type processing, as an example.
Ablative material removal is especially useful for medical purposes, either in-vivo or on the outside surface (e.g., skin or tooth), as it is essentially non-thermal and generally painless. Ablative removal of material is generally done with a short optical pulse that is stretched amplified and then compressed. A number of types of laser amplifiers have been used for the amplification.
Laser machining can remove ablatively material by disassociating the surface atoms and melting the material. Laser ablation is efficiently done with a beam of short pulses (generally a pulse-duration of three picoseconds or less). Techniques for generating these ultra-short pulses (USP) are described, e.g., in a book entitled “Femtosecond Laser Pulses” (C. Rulliere, editor), published 1998, Springer-Verlag Berlin Heidelberg New York. Generally large systems, such as Ti:Sapphire, are used for generating ultra-short pulses.
The USP phenomenon was first observed in the 1970's, when it was discovered that mode-locking a broad-spectrum laser could produce ultra-short pulses. The minimum attainable pulse duration is limited by the bandwidth of the gain medium, which is inversely proportional to this minimal or Fourier-transform-limited pulse duration. Mode-locked pulses are typically very short and will spread (i.e., undergo temporal dispersion) as they traverse any medium. Subsequent pulse-compression techniques are often used to obtain USPs. Pulse dispersion can occur within the laser cavity so that compression techniques are sometimes added intra-cavity. A diffraction grating compressor is shown, e.g., in U.S. Pat. No. 5,822,097 by Tournois. Pulse dispersion can occur within the laser cavity so that compression (dispersion-compensating) techniques are sometimes added intra-cavity. When high-power pulses are desired, they are intentionally lengthened before amplification to avoid internal component optical damage. This is referred to as “Chirped Pulse Amplification” (CPA). The pulse is subsequently compressed to obtain a high peak power (pulse-energy amplification and pulse-duration compression).
As a result, there is a need for a method of improving solid-state laser amplifiers through the modification of the surfaces of the disks and modifications into the surfaces of the disks to a significant depth.